Vasoocclusive devices are surgical implants placed within blood vessels or vascular cavities, typically by the use of a catheter, to form a thrombus and occlude the site. For instance, treatment of a stroke or other such vascular accident may include the placement of a vasoocclusive device proximal of the site to block the flow of blood to the site and alleviate the leakage. An aneurysm may similarly be treated by introduction of a vasoocclusive device through the neck of the aneurysm. The thrombogenic properties of the vasoocclusive device causes a mass to form in the aneurysm and alleviates the potential for growth of the aneurysm and its subsequent rupture. Other diseases, such as tumors, may often be treated by occluding the blood flow to the tumor.
There are a variety of vasoocclusive devices suitable for forming thrombus. One such device is found in U.S. Pat. No. 4,994,069, to Ritchart et al., the entirety of which is incorporated by reference. That patent describes a vasoocclusive coil that assumes a linear helical configuration when stretched and a folded convoluted configuration when relaxed. The stretched configuration is used in placement of the coil at the desired site and the convoluted configuration occurs when the coil is ejected from the catheter and the coil relaxes.
There have been increasing needs to increase the inherent thrombogenicity of these devices. One way of increasing that thrombogenicity is to increase the amount of fiber found in the device. U.S. Pat. No. 5,226,911, to Chee et al., describes a vasoocclusive coil with attached fibrous elements. The fibers are looped in a generally serpentine manner along the coil. The fibrous loops are affixed to (or looped through) the coil at spaced intervals along the coil. The use of multiple fibrous windings is noted in the patent but that use is said to involve placement of the fibers 180.degree. apart on the circumference of the coil.
It should be noted that additional filaments on the exterior of the coil increase the friction of the fibrous coil against the catheter lumen. Added filaments increase the desired thrombogenicity. It is this balance which is difficult to make. We have found a way to increase the overall thrombogenicity without substantially affecting the friction of the inventive coil against the deployment catheter.